The present invention relates to the field of snow-making. More particularly, it relates to improvements in methods and apparatus for producing man-made snow from water only, i.e., without the additional use of either compressed air or high-speed fans.
Various methods and apparatus have been devised over the years for assisting Mother Nature in producing snow at ski resorts and the like. More recently, such snow-making methods and apparatus have even been used at water-treatment facilities for converting winter waste-water to snow which takes the place of a secondary treatment usually required for such water. To date, most man-made snow has resulted by suitably combining air and water under certain favorable conditions. Typically, man-made snow is produced by propelling a relatively fine spray of water particles into the air while cooling the water particles with a rush of turbulent air, as provided by either a source of compressed air or by a high-speed, motor-driven fan. Ideally, the air passing through the spray causes the temperature of the water particles to quickly fall below a critical temperature at which ice crystals (i.e. man-made snow) form from each particle. Whether or not such crystallization occurs, as well as the xe2x80x9cqualityxe2x80x9d of such crystallization, depends on several factors. These factors include (i) water particle size, (ii) ambient atmospheric conditions (viz., temperature, relative humidity and wind speed), (iii) xe2x80x9chang-timexe2x80x9d or flight-time of the particles before settling to earth, and (iv) the velocity of the turbulent cooling air passing through the water spray.
Water particle size is particularly relevant to the snow-making process since, from a physics standpoint, a relatively small particle (i.e., a particle having a relatively small mass and small surface area through which cooling can occur) can be more quickly cooled than a larger particle (with a correspondingly larger mass and surface area). Note, the surface area of the particle increases with the square of the particle""s diameter. Particle size is determined by both the physical characteristics of the nozzle(s) used to produce the water spray, and the water pressure applied to such nozzles. Generally speaking, the smaller the diameter of the nozzle orifice through which water is projected, the smaller the median diameter of the water particles produced. On the other hand, the greater the water pressure applied to the orifice, the smaller the water particles produced. Ideally, the water particles created to produce man-made snow should be sufficiently small to facilitate a rapid conversion to ice crystals, but not be so small as to allow the particles to be either (a) wind-blown from the intended region of snow accumulation, or (b) evaporated in the ambient air, in which case the particles convert to water vapor rather than forming ice crystals.
Equally as important as particle size to snow-making are the ambient atmospheric conditions under which air and water particles are combined to produce snow. Of course, the colder and drier the ambient atmosphere, the easier it is for water particles to convert to ice crystals. Since water normally freezes (crystallizes) at a wet bulb temperature of 32xc2x0 Fahrenheit (0xc2x0 Centigrade), the closer the initial temperature of the propelled water particles to the freezing temperature, the faster the conversion from water particles to ice crystals. Further, the colder and drier the conditions, the better the quality of the snow deposit, assuming a dry, powdery snow is what is desired. Warm, wet conditions give rise to an undesirable, moisture-laden snow pack in which a large percentage of water particles have not been frozen.
Wind speed is relevant to the snow-making process due to its effect on a particle""s xe2x80x9chang-timexe2x80x9d, i.e., how long a particle stays airborne after being propelled into the air. Obviously, the longer a particle remains air-borne, the better its chance for attaining the temperature change required for crystallization. But a wind speed too high is detrimental to snow-making in that the snow deposit may not occur at the desired location. Particle hang-time also depends on (a) the water pressure applied to the water nozzle, the higher the pressure, the longer the hang-time, (b) the elevation of the water nozzle above ground level, and (c) the direction in which the water spray is directed relative to ground level. Usually, to enhance the hang-time of water particles, the snow-making apparatus is mounted atop a tower, typically measuring between 3 and 12 meters, and the water spray is directed upwardly from horizontal to provide for a relatively long particle flight time even on a still day.
Finally, the speed of the cooling air (provided by either a compressed air source or a rapidly rotating fan blade) passing through the water spray determines, in large part, the particle-to-crystal conversion efficiency. The turbulent cooling air operates to quickly transport thermal energy (via convection and evaporation) from the water particles, and the faster the air flow, the greater the number water particles converted to ice crystals, and the larger the size of water particle that can be converted.
It is well known that the production of ice crystals in a water spray can be dramatically enhanced by increasing, within the spray, the number of xe2x80x9cnucleation sitexe2x80x9d (i.e., sub-micron and micron-sized particles) about which crystallization commonly occurs. It is well established that water particles containing a nucleation site (e.g. a dust particle or a small mineral particle in the water) will form an ice crystal more readily than water particles having no such site. Thus, it is common in the field of snow-making to introduce a relatively large number of nucleation sites into the water used to make snow. The introduction of nucleation sites can be effected by either (a) injecting the nucleation sites into the water supply prior to producing the water spray, or (b) injecting the nucleation sites into the water spray after the fact. With regard to the first approach, two commercially available products that operate, when added to a water supply, to supplement the nucleation sites in a water spray produced from such supply are Snomax(copyright) Snow Inducer (made and sold by York International), and Freezyme Snowmaker (made and sold by Samyang Genex). Both of these products comprise tiny microorganisms (dead) that are adapted to be mixed with water to form a concentrated suspension that can then be injected, in metered amounts, into the water supply as snow is being made.
As regards the second approach (noted above) of injecting nucleation sites into a water spray made from a water supply containing no artificial sites, reference is made to the commonly assigned U.S. Pat. No. 5,884,841 to Ratnik et al. This patent discloses a snow-making apparatus in which tiny, micron sized, particles of ice (nucleation sites) are injected into a bulk water spray by a plurality of external xe2x80x9cnucleatorsxe2x80x9d, i.e. nuclei-producing devices, that are positioned at equally-spaced locations outside the water spray, The bulk water spray itself is produced by one or more water nozzles, each having a single orifice or hole through which a flat or conical spray of water particles is produced. Each orifice is sized to produce a spray of water in which the median diameter of the water particles is preferably no greater than about 300 microns when a water pressure of about 500 pounds/inch2 (PSI) or 170 Kg./cm2 is applied. This translates to a nozzle hole diameter of about 0.11 inch (2.8 mm.). Note, recent developments of the bulk water nozzle used in this system have included the addition of up to twelve orifices per nozzle, such orifices being arranged in a circular pattern and oriented to direct their individual sprays of water particles in diverging directions to prevent their immediate interaction with each other (which would otherwise result in the formation of larger droplets). The individual orifices of this nozzle have been as small as 0.046 inch (1.17 mm.), which gives rise to water particles having a median particle size between 132 and 179 microns, depending on the applied water pressure (between 600 and 300 PSI, respectively). Each of the aforementioned nucleators comprises the combination of a relatively small, single orifice, water nozzle, and a small compressed air nozzle. The water nozzle of each nucleator serves to project a fine mist of water particles into the air, and the compressed air nozzle serves to simultaneously cool such water particles in the mist, thereby converting them to tiny ice crystals. The force and direction of the compressed air also serves to inject such tiny ice crystals into the main water spray, thereby providing the desired nucleation sites for the water droplets in the spray to convert to ice crystals. The compressed air also has an inherent cooling effect on the water particles of the bulk water spray that further facilitates crystallization. Compared to other snow-making systems, this particular system is considered highly advantageous from the standpoint that it converts a relatively high volume of water to snow with relatively little use of compressed air, the latter being the most costly ingredient of snow-making. Note, in this apparatus, the only compressed air required is that used to produce and inject the ice nuclei into the water spray. Further, there is no need for a snow-inducer (e.g. the above-noted biological water-additives) to produce an abundance of snow.
In making snow by the conventional methods alluded to above, the need for compressed and/or fan-driven air as a catalyst to the droplet-cooling process has always been problematic. Not only are compressed air sources and/or large, motor-driven fans costly to produce, maintain and operate, they are also difficult to transport up and down mountainsides. Moreover, the need for fast-moving air presents a noise problem, as anyone will attest who has ever been in close proximity to an operating snow gun. Thus, it would be highly desirable to eliminate all-together the use of supplemental air in the snow-making process, or at least, require its use only under the marginal atmospheric conditions in which snow-making has always been difficult, at best, (e.g., at wet bulb temperatures above about 25 degrees F.).
It is acknowledged that, at different times during the development of the snow-making industry, attempts have been made at providing a snow-making system in which water alone is used to make snow. One such system that has been recently commercialized is the xe2x80x9cWaterStick(trademark) Water-Only snow-making system made and sold by York Snow, Inc. This system requires the use of a nuclei-seeded water supply, e.g. a water supply in which the above-noted Snowmax snow inducer has been added, The system hardware (illustrated in FIG. 1) simply comprises a relatively long water pipe 10 having three water nozzles 12 mounted in a cap 14 that encloses one end of the pipe. The water pipe is a common 3 inch (7.5 cm.) diameter aluminum pipe, about 25 to 35 feet (8 to 11 meters) in length. In use, the pipe is arranged in a vertical orientation to position the nozzles at a relatively high elevation that provides for a relatively long flight-time for the water particles projected into the atmosphere by the nozzles. As shown, each of the nozzles is tilted upwards in the cap so as to direct the water spray WS further upwards relative to a horizontal plane. Each of the three nozzles has but a single oval-shaped hole 16 or orifice through which the water particles are projected, and the hole is structured so as to project the water spray through an angular range of about 50 degrees. The hole in each nozzle is centered in a V-shaped notch 18 that serves to produce a relatively flat water spray. To adjust for different ambient conditions, the nozzles are readily removable from the cap 14 so that a change in hole size can be readily effected. In the Waterstick system, the nozzle holes can vary in nominal diameter from about 0.109 inch (2.77 mm.) to about 0.188 inch (4.70 mm.) Thus, on a relatively cold day (say, less than 15 degrees F. wet bulb temperature), a nozzle with the largest hole size would be selected. Such a hole size is desirable from the standpoint that it will provide about three times the throughput (capacity) of the smallest nozzle hole provided (e.g., about 19 gallons per minute (GPM) at 400 PSI for a 4.70 mm. hole, versus only about 6 GPM at the same water pressure for a 2.77 mm. hole). The disadvantage of using a large nozzle hole, of course, is that, for a given water pressure, it produces a spray comprising much larger water particles than does a smaller nozzle hole. For example, at a water pressure of 400 PSI, the median water particle size projected by the largest Waterstick nozzle is about 440 microns, versus a median particle size of about 380 microns for the smallest nozzle. While water particles in this size range will crystallize without an assist from compressed air or the like when projected from high elevations (e.g., above 10 meters) and at low ambient wet bulb temperatures (e.g., less than 15 degrees F.), such particles cannot be converted to snow at ambient wet bulb temperatures higher than 20 degrees F., and/or when the particles are projected from elevations much lower than 10 meters. While somewhat smaller water particles can be achieved with the Waterstick nozzles by increasing the applied water pressure from 400 to, say, 600 PSI, the smallest median particle size achievable at this pressure is only about 270 microns, that being with the smallest nozzle size(0.109 inch). But even with particle sizes this small, it is not possible to make snow with the WaterStick system at ambient wet bulb temperatures above about 19 degrees F., even were the spray to be produced at an elevation of 12 meters. Note, while the WaterStick cap supports a total of three nozzles and, hence, can theoretically achieve a throughput three times that of a single nozzle, it has been found that, except at extremely low ambient temperatures, the center nozzle must be deactivated (i.e. plugged); otherwise, the xe2x80x9cbloomxe2x80x9d of snow projected by the nozzles becomes highly saturated with water, resulting in the production of a heavy, moisture-laden snow deposit. Thus, while the WaterStick System does, in fact, operate to produce snow without the use of any compressed air or fan, it does so under relatively restricted atmospheric conditions, e.g. requiring an ambient wet bulb temperature of at most 19 degrees F., and an elevation of at least 8 or 9 meters. Further, using only single-hole nozzles, the capacity of this system is relatively limited in terms of gallons of water converted to snow per minute.
In view of the foregoing discussion, an object of this invention is to provide an improved method and system for making snow without the use of either compressed air or high speed, motor-driven fans and the like.
Another object of this invention is to significantly expand the conditions under which man-made snow can be produced without the use of either compressed air or high speed fans, and to substantially increase the snow-making capacity of such systems.
Still another object of this invention is to provide a new water nozzle, when used in a water-only snow-making system, enables the system to operate effectively at warmer ambient temperatures and from elevations relatively close to the ground.
In accordance with the present invention, it has been found that, by using a water nozzle of the type described herein in a water-only snow-making system of the type described herein, the throughput of the system, compared to conventional systems, can be significantly increased (by as much as a factor of five). Further, by virtue of the invention, snow can be produced from water only at significantly higher ambient wet bulb temperatures than is possible with conventional water-only systems (e.g., 5 degrees F. warmer) and at elevations significantly closer to ground level (i.e., about one-half the elevation required by conventional systems), thereby better assuring that the snow is deposited when and where it is desired.
According to a first aspect of the invention, a preferred water-only method for producing snow comprises the steps of: (a) pre-seeding a water supply with artificial nucleation sites about which water particles produced from such supply and containing such artificial nucleation sites can crystallize; (b) filtering the pre-seeded water supply to filter out solid particulate matter of a size 0.015 inch (0.38 mm.) and larger; (c) providing a water nozzle having a plurality of spaced holes, each hole measuring between about 0.030 inch (0.75 mm.) and 0.040 inch (1.0 mm) in diameter; (d) supporting the nozzle at a level of at least 10 feet (3 meters) above ground level; and (e) directing the filtered and pre-seeded water through the nozzle holes at a pressure of between about 250 and about 800 PSI to produce a plurality of water sprays, each spray containing water droplets having a maximum median diameter of between about 100 and about 170 microns.
According to a second aspect of the invention, a preferred water-only system for producing snow comprises (a) a pre-seeded water supply having artificial nucleation sites about which water particles produced from such supply and containing such artificial nucleation sites can crystallize; (b) a filter for filtering out solid particulate matter of a size 0.015 inch (0.38 mm.) and larger from the pre-seeded water supply; (c) a water nozzle having a plurality of spaced holes, each hole measuring between about 0.030 inch (0.75 mm.) and 0.040 inch (1.0 mm) in diameter; (d) a tower for supporting the nozzle at a level of at least 10 feet (3 meters) above ground level; and (e) a pump for projecting the filtered and pre-seeded water through the nozzle holes at a pressure of between about 250 and about 800 PSI to produce a plurality of water sprays, each spray containing water droplets having a maximum median diameter of between about 100 and about 170 microns. Preferably, the water nozzle has at least sixteen holes through which water is projected arranged in a circular array, each hole being spaced from an adjacent hole by at least 0.25 inch (6.25 mm.).
According to a third aspect of the invention, a new and improved water nozzle is provided that is especially adapted for use in a water-only snow-making system. The nozzle comprises a housing defining a plurality of spaced holes. Owing to the size of the holes, the nozzle is capable of producing water particles of a size that will readily crystallize at wet bulb temperatures as high as 25 degrees F. when projected into the air from an elevation less than about 25 feet (8 meters). Owing to the number of holes, the nozzle provides a throughput or capacity, in terms of the volume of water converted to snow per unit time, significantly greater than the throughput of conventional nozzles used in water-only snow-making systems, Preferably, each of the holes has a nominal diameter of between about 0.030 and about 0.040 inches (about 0.75 to about 1.0 mm.) Preferably, the number of holes per nozzle is sixteen or more, and the holes are arranged in one or more circular arrays having nominal circle diameter of at least about 1.75 inches (44.5 cm.). Preferably, the spacing between adjacent holes in the circular array is at least 0.25 inches (6.3 mm.), and more preferably at least 0.35 inches (9 mm.). When two or more circular arrays of holes are used, the holes are preferably arranged to form two or more concentric circles.
The invention and its advantages will be better understood from the ensuing detailed description of preferred embodiments, reference being made to the accompanying drawings In which like reference characters denote like parts.